Roots 127 



and the vegetable mould and sand a fraction over 

 twelve and a quarter per cent. 



The supply contained in the sand was exhausted 

 first, of course, because it contained so much less to 

 start with ; but, though the other soils were not nearly 

 as dry, the plants flagged because they could not get 

 hold of the water which they still contained. 



Some plants, such as rice, grow equally well in soil 

 or water, but most plants are injured by having their 

 roots kept in water for any length of time, and are, as 

 a rule, in better health when allowed to take up the 

 moisture they need from that which is contained, 

 invisibly, in the pores of the soil, when it does not look 

 actually wet at all, and no moisture could be squeezed 

 out of it. 



But our main point now is to show that soil may, 

 and does, become damp without rain. It may be dried 

 by sun and wind by day, but it makes up for this by 

 drawing moisture from the air by night, and it is this, 

 partly, which enables plants at least to live through a 

 time of drought, though their very stunted growth 

 shows that the supply has been insufficient for their 

 needs. 



The moisture which the soil thus draws from the air 

 does not remain on the surface, but, like the rain and 

 dew, sinks into the ground, penetrating deeper and 

 deeper, and moistening the soil until it is used up, or 

 stopped by meeting either with damp soil, or with soil or 

 rock through which it cannot pass. Rain falling upon a 

 porous soil, such as sand, or even soil containing much 

 sand, passes quickly through it until it meets with a 

 bed of stiff clay or rock, which prevents its going 

 further ; and then what is left, over and above what the 



